Water adsorption and capillary bridge formation on silica micro-particle layers modified with perfluorinated organosilane monolayers.

Graphical abstract Highlights • Combination of QCM-D and in-situ reflection FTIR spectroscopy. • Comparison of water adsorption on smooth films and particle layers. • Distinction of water adsorption on surfaces and contact points of particle layers. • Monomolecular surface functionalization of SiO 2 -particle layers by perfluorinated molecules. Abstract Monodisperse micron-sized silica particle monolayers deposited onto plasma-grown SiO x -ultra-thin films have been used as reference systems to investigate wetting, water adsorption and capillary bridge formation as a function of silica surface functionalization. 1H,1H, 2H,2H perfluorooctyltriethoxysil (FOTS) monolayers, have been deposited on the respective surfaces by means of chemical vapor deposition resulting in macroscopically low energy surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) reflection absorption spectroscopy confirmed the monolayer formation. Water adsorption isotherms were studied by a combination of in-situ FTIR reflection spectroscopy and quartz crystal microbalance (QCM) while macroscopic wetting was analysed by contact angle measurements. The comparative data evaluation indicates that the macroscopic wetting behaviour was changed as expected, however, that water nanodroplets formed both at intrinsic defects of the FOTS monolayer and at the FOTS/SiO x interface. Capillary bridges of liquid water are dominantly formed in the confined particle contact areas and between surface asperities on the particles. The comparison of wetting, adsorption and capillary bridge formation shows that the hydrophobization of porous materials by organosilane monolayers leads to the formation of morphology dependent nanoscopic defects that act as sites for preferential capillary bridge formation. [ABSTRACT FROM AUTHOR]